Semiconductor memory is used in a variety of applications. One of the most useful and widely employed types of semiconductor memory is SRAM, or static random access memory. As long as power can be continuously supplied to the cells of an SRAM array, this type of semiconductor memory allows fast access for both reading and writing individual memory cells.
In some applications, SRAM cells in a secondary array are used as a status indicator (e.g., cell validity) for corresponding memory cells in a primary array. For example, a given SRAM cell can be set to “1” when the corresponding memory cell in the primary array is deemed “valid”; prior to this event, the given SRAM cell will be expected to carry the value “0”, thereby indicating that the corresponding primary cell is invalid. The use of a secondary SRAM array thus allows an external entity to rapidly access information about the validity of the cells in the primary array without having to access the primary array. This can be useful when the primary array is manufactured using a type of memory that may not allow individual cells to be as flexibly or as quickly accessed as in SRAM.
However, because SRAM cells acquire an unpredictable value upon power-up, an initialization (“preset”) operation is required in order to guarantee that the given SRAM cell will indeed carry the value “0” before being written to with a “1”, or vice versa. Applying this initialization operation to all SRAM cells in an array can lead to a cumbersome and lengthy preset phase.
It will be appreciated that a preset phase is required in many applications involving the use of SRAM. Improvements in the area of presetting the cells of a semiconductor memory array are therefore welcome.